Tetrafluoroethylene, ionization

Copolymerization is effected by suspension or emulsion techniques under such conditions that tetrafluoroethylene, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible, because of heat-transfer limitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). 

Fluorocarbon elastomers, particularly copolymers of HFP and VDF, are cross-linked by low-level y radiation (up to 20 Mrad) in the same fashion as PVDF. Radiation degradation of a VDF-HFP copolymer was studied by Zhong and Sun.35 Their finding was that there is a linear relationship between the dose and the weight loss of the polymer. Fluorocarbon elastomers based on copolymers of IFF and propylene were found to be more resistant to y radiation than Viton elastomers.36 Cross-linking of VDF-HFP, VDF-TFE, and tetrafluoroethylene-propylene (TFE/P) copolymers as well as of terpolymers VDF-HFP-TFE by ionizing radiation (gamma... 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

We have just derived D (C2F4) D (C2H4) 174 kcal mol 1. As befits the "perfluoro" and "7r-fluoro" effects on "normal", closed-shell species, we expect that the ionization potential of tetrafluoroethylene, the parent hydrocarbons, and the various fluorinated species to be "similar." Table II, with all its numbers in eV, documents this. 

Radiation-induced curing of plastic coatings has been discussed,8 and radiation-induced polymerization in the solid state reported.87 The radiation chemistry of epoxy-containing electron resists88 and polycondensation induced by ionizing radiation in the urea-formaldehyde system88 have been described. Radiation-induced copolymerization of the following pairs of monomers has been achieved ethylene-hexafluoropropylene,80 tetrafluoroethylene-propylene,81 tetrafluoroethylene-hexafluoropropylene,82 hexafluoroacetone-a-olefins,83 MMA-di- and tri-methacrylates,84 styrene-acrylonitrile,85 buta-1,3-diene-acrylonitrile,88 and acenaphthylene-vinylcarbazole.87... 

While a munber of alternative polymer membranes have been developed. Nation is still considered the benchmark of proton conducting polymer membranes, and has the largest body of research hterature devoted to its study. Alternative polymer membranes are almost invariably compared to Nation . Nation is a free radical initiated copolymer consisting of crystaUiz-able, hydrophobic tetrafluoroethylene and a perfluorinated vinyl ether terminated by perfluorosulfonic acid. Nation 117 possesses an equivalent weight of 1100 (EW = mass of dry ionized polymer (g) in the protonic acid form that would neutralize one equivalent of base). Thus, there are 13 perfluoro-methylene groups (-CF2-) ( = 6.5) between pendent ionic side chains. 

J.J. Lu, Z. Zhu, W. Wang, S. Liu, Coupling sodium dodecyl sulfate-capillary polyacrylamide gel electrophoresis with matrix-assisted laser desorption ionization time-of-flight mass spectrometry via a poly(tetrafluoroethylene) membrane. Anal. Chem. 83 (5) (2011) 1784-1790. 

A combination of gas chromatography and either electron-impact or chemical ionization mass spectrometry has been used to analyse the products of thermal degradation of poly(vinyl fluoride) and of a number of other polymers [poly(vinyl chloride), aromatic polyimides, polyurethane]. The degradation of poly(vinyl-idene fluoride) has been related to its crystalline form. It is claimed that dehydrofluorination may take place preferentially in crystalline segments containing trans sequences. Thermo-oxidative breakdown is modified if vinylidene fluoride is copolymerized with tetrafluoroethylene or hexafluoroacetone. Dehydrofluorination occurred in both copolymers, but in the latter it was preceded by cleavage of the H from the CHj group in the alpha position to the ether bond followed by scission of the C-0 bond. ... 

Apart from the fluoro monomers vinyl fluoride (VF), vinylidene fluoride (VF2), and tetrafluoroethylene (TFE), only chlorofluoroethylene has found commercial use as homopolymer. It is applied as thermoplastic resin based on its vapor-barrier properties, superior thermal stability (Tdec > 350 °C), and resistance to strong oxidizing agents [601]. Chlorofluoroethylene is homo- and copolymerized by free-radical-initiated polymerization in bulk [602], suspension, or aqueous emulsion using organic and water-soluble initiators [603,604] or ionizing radiation [605], and in solution [606]. For bulk polymerization, trichloroacetyl peroxide [607] and other fluorochloro peroxides [608,609] have been used as initiators. Redox initiator systems are described for the aqueous suspension polymerization [603,604]. The emulsion polymerization needs fluorocarbon and chlorofluorocarbon emulsifiers [610]. 

Polymer destruction initiated by ionizing radiation is accompanied by the formation of double bonds and by the evolution of gaseous products (hydrogen, low-molecular-weight hydrocarbons, hydrochloric acid, tetrafluoroethylene, etc.). In the presence of oxygen, oxidized structures such as hydroperoxides. 

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